U.S. Pat. No. 6,554,333 discloses a shock absorber comprising an elongated hollow body with a revolution shape with respect to an axis and defining different stepped tube sections of decreasing diameters. Between every two tube sections of different diameters, there is a transition section defining a step with a perimetric wave provided to facilitate the telescopic insertion of one section into the other in case of impact. The end of the larger diameter tube section is joined by welding to a connection plate or member adapted to be fixed in a releasable manner to the vehicle structure. The end of the smaller diameter tube section is inserted in a hole of the bumper crossbeam and joined thereto by welding. The shock absorber is obtained by the plastic deformation of a straight metal tube which is enlarged or reduced in diameter in order to form the different tube sections. The patent does not mention the plastic deformation forming technique used to form the shock absorber.
U.S. Pat. No. 6,854,5754 describes a shock absorber comprising an elongated tubular body with two stepped diameter tube sections, obtained by the plastic deformation of a straight tube. The larger diameter tube section is provided to be joined to a part of the frame of the vehicle and a smaller diameter tube section to be joined to a bumper crossbeam. The tubular body defines a first tube section of a first larger diameter, a second tube section of a second diameter that is smaller than the first one, a step section connecting said first tube section and said second tube section by means of a wavy annular step with an S-shaped cross-section.
U.S. Pat. No. 6,908,129 describes a shock absorber for an automobile comprising an elongated tubular body with several stepped tube sections of decreasing diameters. In an embodiment described in the figures, the elongated tubular body defines two tube sections of different diameters and a stepped section defining a wavy annular step with an S-shaped cross-section. In order to install the shock absorber in a vehicle, the end of the larger diameter tube section is joined to a flat plate perpendicular to the axis of the tubular body.
U.S. Pat. No. 7,021,686 describes another example of a shock absorber for a vehicle based on a tubular body with several tube sections of different diameters or stepped widths.
The shock absorbers described in the patents mentioned above have a substantially constant wall thickness in all the tube sections. A shock absorber in which at least one of the tube sections, such as for example the smaller diameter tube section, had a thickness less than the thickness of the wall of the larger diameter tube section with the purpose of optimizing the weight of the shock absorber and providing a greater resistance only in those tube sections requiring it would be desirable.
Document JP-A-2000240707 discloses a shock absorber comprising a tubular body having a constant inner diameter and two sections of decreasing outer diameter such that it includes a first cylindrical section with a thicker wall, a second cylindrical section with a thinner wall and a transition section between both. The mentioned tubular body is obtained by cylindrical lathe spinning.
Patent DE-A-10002379 describes a one-piece shock absorber having at least two length sections of decreasing cross sections telescope-like arranged and mutually connected through a shoulder. The first length section has a flange and the second length section has a free end closed with an end side. The first and second length sections are arranged along a longitudinal axis and exhibit respective flat sides. The shock absorber is obtained by a deep-drawing procedure, and thereby the thickness of the flange is larger than the wall thickness of the length sections, the greater thickness of the flange providing reinforcement for the flange serving as a mounting surface.
Patent DE-A-19814842 discloses a damping device, capable of absorbing the impact force from frontal, rear and/or side collisions, comprising a hollow body made by deep drawing from sheet metal, plastic or composite material. The sides of the hollow body are deformed by a high pressure procedure to form curved bulges extending in a ring-shape around the body length axis. In an exemplary embodiment, a one piece blank is used to form the hollow body, said blank including a plate, an elongated hollow portion extending from said plate, and an end wall closing at least in part one end of said provisional hollow portion opposite to the plate. An upper section of said elongated hollow portion has a thickness that is thinner than the thickness of a lower section of the elongated hollow portion and the plate.
The shock absorbers of the documents of the prior art mentioned above for connecting to a frame of the vehicle and/or to the bumper crossbeam must be joined by welding to connection parts or directly joined by welding to the frame and/or bumper crossbeam. The weld joining operation can create stress in the assembly that can negatively affect the resistance and/or the behavior of the shock absorber.
Therefore, there is a need for a one piece shock absorber provided with an elongated hollow portion connected at one end to a plate and at least partially closed at the other end with an end wall, wherein at least part of the elongated hollow portion has a thickness thinner than the thickness of the plate, and wherein the shock absorber is able to be produced from a metal sheet portion by a two step method including a spinning technique.